1. Field of the Invention
The present invention relates to an electronic device including a computer system incorporating a disk subsystem, a disk array, or a disk drive. The present invention also relates to a technology, which allows high-speed transfer by means of arrayed disks connected by a fabric switch.
2. Description of the Prior Art
In general, the connection between a disc controller device and a plurality of disk drives in a disk array may be achieved, as disclosed in the JP-A No. 10-171746, by an SCSI interface or by a fibre channel arbitrated loop topology.
The SCSI interface, which uses a time-divided data transfer method on one signal line, negotiates with its initiator one to one for one moment on one signal line for an access.
The fibre channel arbitrated loop topology, on the other hand, may connect the initiator and disk drives in a loop by means of a serial interface, to enable time-division transfer of the data divided into frames to allow a number of communications with a plurality of devices at the same time and to allow up to 126 disk drive devices to be connected.
Disk drives will become more and more compact and higher density implementation thus will ultimately realize the use of more disk drive devices. Ideally the connection of a disk drive with its interface one to one should be implemented to enable a maximum transfer rate.
An SCSI interface in the Prior Art adopts a one-to-one data transfer scheme for one moment in one signal line. This may be a drawback if one wishes to implement simultaneous communications between an initiator and a plurality of disk drives. The number of connectable disk drive units in one bus is also limited to 7 or 15. When one connects a number of drive units for one-to-one negotiation on the SCSI interface, a plurality of interfaces are required, causing difficulty in mounting. Because the number of the connectable disk drive units in one controller is so limited, one may encounter the necessity to add some further controller interfaces for connecting all units to a system.
When using a fibre channel, a plurality of disk drive units may be connected to a single controller. In a case where the controller and disk drive units may be connected by implementing a fibre channel fabric switch for switching the connectivity, a substantial one-to-one connection between the controller and the disk drive units may be implemented. Although the controller may support a fabric protocol for switching connection, generic disk drive units support only a fibre channel arbitrated loop (FC-AL) protocol but not the fabric protocol.
This resulted in that the switching connection may not be implemented, so that a loop connection had to be used with the FC-AL for sharing a same loop between plural disk drive units.
More specifically, a device (a controlling device in this context) which supports the fabric protocol has a World Wide Name (WWN), as its unique 24-bit address. The device may be logged in to the fibre channel fabric switch by using this unique address. A device (a disk drive unit) which supports only the FC-AL protocol but not the fabric protocol uses significant 16 bits in a same 24 bit address for verifying location within the loop and least 8 bits for the address AL-PA (Arbitrated Loop Port Address: each disk unit have a unique value in the loop) for logging in to a device (a controlling device managing the loop).
In such a loop connection, if the number of disk drive units connected in the same loop is increased, a data transfer rate of disk drive units may ultimately exceed beyond a maximum data transfer rate of the loop, resulting in that the data transfer in this loop may be limited to efficiency of the maximum data transfer rate of the loop. The data transfer rate in such a loop will be decreased to that in an equivalent SCSI interface.